Aircraft



Feb. 21, 1928. 1,659,960 A. ROHRBACH AIRCRAFT Filed July 14. 1924 fect of all controls at the same time Patented Feb. 21, 1928.

UNITED STATES PATENT OFFICE.

.uncnarr.

Application filed July 14, 1924, Serial No. 725,834, and in Germany December 18, 1923.

It is a well known fact that too low a flying speed greatly endangers an airplane. A diminishing speed relative to the surrounding air is accompanied by an 1ncrease 5 in the angle of incidence of the wings and it too often happens that the l1m1t is reached, where the air-flow round the wing undergoes such a change, that the clrculating current, producing the lift force, cannot increase in intensity with increasing angles of incidence. In this case air-flow no longer suflices to sustain the aircraft in normal flight, the speed being too low and the angle of incidence too large, and the stalled aircraft begins to lose height, its

resultant movement being composed of the remaining flying movement and the falling movement. dangerous because of its instability, the cfbeing so small, when compared with the resulting unstable forces, that it is often difficult to effect a return to normal flight.

Speed-indicators and similar instruments have been provided for indicating to pilots the speed conditions of the craft, but experience has taught that a pilot, becoming aware of some obstacle in front, is often tempted to yield to his natural impulse and ap-' proach the dangerous place at the slowest possible rate, thus stalling the aeroplane and crashing down owing to a too great decrease of speed.

Then attempts have been made to change 1 the qualities of the wings by means of slots or flaps or similar measures allowing the in tensity of circulation or lift to increase up to very large angles of incidence, thus enabling the ilot to alight at a considerably 0 lower spee This, .however, means but a shifting of the perilous zone. The pilot, getting accustomed to this new arrangement, will probably cause a sudden fall of the plane by excessive stalling of the machine at the newly established limit.

Considerable longitudinal stability of the craft, eflected for example by correspond ingly long fuselages and large horizontal tail planes, tends to prevent the pilot from taking perilously large angles of incidence, but there is a considerable drawback to such a great longitudinal stability in that the controllability of the plane is unduly im- The resulting motion is most arms 24 carried by the paired and pronounced pitching vibrations .are present which create unsatisfactory flying conditions. 7

The object of the invention is to avoid crashes and stalling of an aeroplane due to unduly large angles of incidence and to this end I have provided means independent of the pilot for anticipating unduly'large angles of incidence and enabling the operation of the controls to avoid the perilous angles which are about to be assumed. The invention may assume many forms but the particular embodiment of the invention herein exhibited includes a mechanism which functions to oppose the abnormal operation of the longitudinal controls. Such mechanism includes a control element which is so constructed and arranged as to be sensitive to changes in angles of incidence, such for example as a vane or other element under the influence of a free air current or flow and is responsive to unduly large angles of incidence to oppose the operation when perilous angles-are or are about to be attained;

and in the embodiment of the invention herein exhibited the opposing counteractin or nullifymg action is positively efiected by means under the control of the vane, as for example by an automatically adjustable fin or horizontal surface actin in opposition to the elevator effect when t e latter is operated to unduly largedegrees For abetter understanding of the invention, reference may be had to the accompanying drawing diagrammatically illustrating one embodiment thereof.

Referring to the drawing I have diagrammatically illustrated a part of the longitudinal control mechanism includin an elevator 1 which is pivoted on'the axis 4 for up and down controlling movements. This elevator may be actuated for effecting the lon itudinal control of the aircraft in any sultable manner, as for example by means of the cables 23 fastened to suitable ivoted elevator 1. In the particular embo iment shown the elevator 1 is carried by a normall horizontal fin 2. -At 3 I have indicated a safety rudder or actuating vane which in response to unduly large angles of incidence or angles of incidence approaching a predetermined value, functions to prevent the pilot from stalling the craft. In the particular embodiment illustrated this actuating vane 3 acts in opposition to the pilot by actuating the horizontal fin 2 in opposition to the abnormal movements of the elevator 1. This safety rudder or vane is carried by a main bearer 7 which is pivoted to any suitable stationary part of the aircraft at the axis 6.

- mounted on a stationary axis and carries a slide or guide bolt 13 upon which slides the block 12. A bar is pivotally connected to the slide block 12 at 11 and carries at its upper end a bolt 9 which operates within the slot 8 to lower and elevate the bar 10 in response to control movements,there being a guide 22 diagrammatically illustrated and position near the. upper end of the bar and bolt -9 to properly gulde the u per end of the bar and the bolt 9. The slide block 12 is shifted back and forth along the guide 13 in response to the control of the elevator 1 for the purpose of bringing the block closer to or farther away from the axis 5 of the fin. The mechanism for this purpose is a bell crank lever 14 rejecting from the elevator 1, a pivoted linli connecting link or arm 16 and forked arm 20 carried by the connecting link 16 and embracing the slide block 12. The fork 20 engages the block 12 by means of any suitable connections permitting the rocking back and forth of the fork and the sliding movements of the block, such for example as the rotatory guide pieces 21 disposed on opposite sides of the block, the arms of.

fork 20 catching into these rotatory guide ieces 21 and being guided thereby. The bell crank lever 14, the pivoted link 18 and the connecting link or rod 16 form a sort of parallelogram-like carrier for the forked arm 20 and the latter, by means of the connections generally indicated moves the block 12 back and forth along the guide 13 in response to the actuation and control of the elevator 1. The operation of the mechanism shown is as follows: The safety controlling vane 3 can move freely through small changes and angles of incidence without affecting the control mechanism, since as above indicated that part of the cam slot 8 which is functioning with the bolt 9 and bar 10 during such small changes in angles of incidence is concentricall arranged with reference to the axis 6. arger angles of incidence, on the contrary, due for example to an exessive manipulation of-the longitu- 18 carried by the fin2, a

dinal controls, result in the vane 3 operating the controls or counteracting their effect so as to prevent such unduly large angles of incidence. If, for example, by reason of the excessive upward setting of the elevator 1 the largest permissible angle of incidence of the wings has been reached, the relative position of the craft and the. vane 3 changes so materiall that the rod 10 is pulled up by means of the bolt 9 riding up the cam slot 8,-this upward operation of the bar 10 tending to neutralize correspondingly the action of the elevator 1 by the manipulation of the fin'2 in the opposlte direction. Notwithstanding, therefore, the unduly large controlling movements of the elevator 1, the

aeroplane is then able to maintain ahorizonsmall settings of the elevator 1, however, the

actuating movements of the fin 2 b shifting of the sliding bolt 12 are insi ni cant.

he lengths of all levers and t e form of the curved lengths are so selected that the safety rudder-or actuatin 'vane begins to work at a certain, but yet armless angle of incidence. The pilot is entirely unhindered in pulling or pressing the elevator 1 to attain all ordinar and safe angles of incidence of the wings. owever, as soon as the safety control begins to act, the angle of incidence cannot be increased any further, thereby avoiding accidental stalling of the machine.

The adjusting effect of the fin is chosen in such a manner that'even at the steepest position of the aircraft against the surrounding air, there is still a suflicient reserve in regard -to the angle of incidence to prevent the machine from gettin into the overpulled or stalled condltion uring oscillations or s ualls.

All parts of t e safety control are so arranged and in consonance to each other by the selection of. light building material, by counterbalancing of weights, 1f necessary by means of additional masses, by computation of the friction of the bearings, etc., that the controllin vane accepts exclusively the direction o the free air-flow and is not influenced in its position by an acceleration of the masses as a result of the motion or position of the aircraft.

The vane 3 must be so large, its arm 7 so long, and all of the transmitting agents so arranged, that the horizontal fin 2 re- 'mains perfectlystable in its normal position.

The aircraft with its elevatorand the safety device are then formin in regard to their relative positions a stab e system if the vane is in action, i. e., the aircraft flies with perfect stability'straight ahead with the maximum angle of incidence limited by the safety device. 7

The vane is preferably to be mounted in such proximity to a vertical line imagined in the centre of gravity that in curving flights an approximate mean value is obtained for the air-flow influencin the vane, though other dispositions woul be fairly satisfactor if-properly constructed and a justed. T e best and most satisfactory adjustment of the vane by the air current relatively to the osition of the aircraft would perhaps not e attained, if the vane were situated on a wing tip, and the aircraft turning about this end. Similarly unfavorable conditions might result from an arrangement of the vane at a great distance from the wings, perhaps in the proximity of the tail end of the aircraft. Care must be course be taken that the vane or auxiliary controlling element is not directly exposed to the slip stream of the propeller or unfavorably influenced in some other way.

For the kinematic connection of fin, elevator and vane, other arrangements may also be used. The desired effect may be attained by another auxiliary surface set in place of the horizontal fin without departing from the invention.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. In an airplane, the combination of an elevator for the longitudinal control and a device for actuating said control and effecting the normal control of the craft with, an auxiliary means opposing said elevator control including a vane under the influence of the free air-flow and sensitive to a certain angle of incidence of the craft for counteracting the longitudinal control.

2. u an airplane thecombination of the longitudinal control and means for normally actuating the same unhindered within a certain predetermined safe range with a pivoted vane under the influence of the free airflow and sensitive to an angle of incidence of the craft correspondin to a certain position of said longitudinal control, together with connections between the pivoted vane and the longitudinal control for opposing the action of said control when the latter tain predetermined safe range with a pivoted vane under the influence of the free airflow, together with connections therebetween and the longitudinal control, which permit fiuence of the free air-flow and sensitive to predetermined angles of incidence which is adapted to operate said element, and connections whereby the latter is unaffected by said vane during the normal and predetermined permissible variations in angles of incidence ofthe craft, but operable thereby upon the attainment of an unduly large angle of incidence to reduce the latter.

5. In an aircraft ca able of unhindered.

control within a. pre etermined range of angles of incidence an element to'be operated, -a device which is sensitive toangles of incidence of the craft for operating said element, and connections whereby the latter is unafiected by said device durin the normal and predetermined permissiEle variationsin angles of incidence of the craft, but operable thereby upon the attainment of an unduly large angle of incidence to reduce the" latter.

6. In an aircraft, the combination of a longitudinal control with a mechanism for anticipating and preventing unduly large angles of incidence of the craft before they are reached including a control element sensitive to angles of incidence of the craft and a normally fixed but adjustable horizontal controlling surface together with connections between the said normally horizontal surface and the control element for giving to said horizontalsurface a setting tendin to counteract the effect of the longitudina control at a predetermined angle of incidence as determined by the control element.

7. A control of the character set forth in claim 6 in which the longitudinal control includes an elevator mounted for pivotal movements on the normally horizontal but adjustable surfacel 8. A control of the character set forth in claim 6 wherein the connections between the auxiliary control element and the normall horizontal but adjustable surface are suc that within a predetermined range of variations of angles of incidence the horizontal surface is stably fixed in position while the control element under the influence of the free air-flow is free to follow the direction of the air currents.

9. A control of the character set forth in claim 2 wherein the connections between the pivoted vane and longitudinal control include an actuating cam carried by the vane whose surface is partly concentric and partly eccentric to the ivotal axis of the vane for the purpose set orth.

10. In an aircraft a normall fixed but adjustable longitudinal control e ement, an elevator pivotally'carried by said control element, 9. ivoted vane under the influence of the airow, and connections-between said vane, the control element and the elevator, including a connecting link connected at one end by means of a cam to said vane and at the other end to the normally fixed control element by means of a connection ad'ustable in a direction towards and away rom the pivotal axis of'the control element and connections between the elevator and said sliding connection to shift said connection when the elevator is operated.

' 11. A control of the character set forth in claim 10 wherein the upward settings of the elevator bring the sliding connection nearer the pivotal axis of the normally fixed control element for the purpose set forth.

- 12. A control of the character set forth in claim 13 wherein the safety vane is so arranged with reference to the vertical axis throu h the center of gravity of the aircraft and t e structural parts thereof are arranged, harmonized and balance in such manner that the correct relative positions cannot be altered by acceleration of the masses as a result of motion or position of the aircraft or the correct influence of the air-flow upon the vane is not disturbed.

13. In an aeroplane the combination of a longitudinal control and means for actuating said control unhindered to effect the normal control of the craft, with a controlling wind vane disposed in the free air stream and sensitive to certain angles of incidence of the craft and operative connections therewith, said vane and connections permitting the normal operation of the longitudinal control unhindered but upon the attainment of predetermined angles of incidence operative to oppose the action of the, normal control.

14. In an aeroplane the combination of a longitudinal control and means for actuating said control unhindered to effect the normal control of the craft, with a vane disposed in the free air flow and sensitive to abnormal angles of incidence of the craft and operative means between the controlling vane and the normal control for opposing the action thereof upon the approach of unduly large angles of incidence.

15. In an aircraft the combination of a longitudinal control and means for normally operating said control through a predetermined range of movements unhindered, with a mechanism for anticipating angles of incidence beyond said range including a controlling vane under the lnfluence of the free air flow and sensitive to predetermined angles of incidence, together with'connections, for

opposing the longitudinal controls and preused controls for varying the angle of incidence of the craft and in addition thereto a safet mechanism for preventing the stalling of t e craft, the latter including a comtrolled device which directly affects the flying position of the aircraft and a controlling wind vane which, upon the angle of incidence of the wings approaching a dangerous limit, is responsive to the abnormal angle of incidence and operable by the free air stream to operate said controlled device.

18. An aircraft which is capable of normal longitudinal control movements unhindered within a predetermined range of angles of incidence, including a device for modifying the flying position or attitude of the craft and a controlling wind vane disposed in the free air stream and o erative connections therefor, said vane an operative connections permittin the normal control movements unhindered within said predetermined range of angles of incidence but operable upon the attalnment of an angle of incidence beyond the predetermined range to operate said device and thereby reduce the angle of incidence.

19. In an aircraft the combination of a control surface to be mani ulated and means operating the same for e ecting unhindered certain normal control movements of the craft, with an independent control element which is sensitive and responsive to predetermined abnormal controlmovements of the craft and operative connections for opposing the abnormal control movements.

20. In an aircraft the combination of a controlling vane disposed in the direction of the free air flow, a longitudinal control mechanism ,for controlling the elevation of the craft, and means under the control of the vane for opposing the longitudinal control and preventing unduly large angles of incidence.

Dated this 2nd day of July, 1924. 

